Multi-die module with contactless coupler and a coupling loss reduction structure

ABSTRACT

A multi-die module includes a first die with a first electronic device and a second die with a second electronic device. The multi-die module also includes a contactless coupler configured to convey signals between the first electronic device and the second electronic device. The multi-die module also includes a coupling loss reduction structure.

This application is a divisional of U.S. patent application Ser. No.16/231,555, filed Dec. 23, 2018, the contents of all of which are hereinincorporated by reference in its entirety.

BACKGROUND

The proliferation of electronic devices with integrated circuit (IC)components continues. There are many different IC fabrication andpackaging strategies, each strategy with its own pros and cons. AlthoughIC fabrication technology provides an excellent platform formanufacturing circuits with repeated components, there are unmetchallenges when it comes to manufacturing IC circuits with differenttypes of components. The result of existing IC fabrication limitationsis that IC components are often limited to a particular type ofcomponent and thus multiple IC dies or chips need to be connectedtogether to complete a desired circuit.

While direct coupling of a first device on a first die and a seconddevice on a second die is possible (e.g., using wires, pads, solder,etc.), avoiding direct coupling facilitates packaging. Alternatives todirect coupling include contactless coupling options such as capacitivecoupling and inductive coupling. However, in many scenarios, there areunwanted performance drawbacks resulting from contactless coupling, Asan example, inductive coupling in an oscillator circuit (e.g., between afirst die with a resonator and a second die with an oscillator core)undesirably reduces the quality factor of the oscillator circuit.Efforts to improve multi-die circuit packaging and performance areongoing.

SUMMARY

In accordance with at least one example of the disclosure, a multi-diemodule comprises a first die with a first device and a second die with asecond device. The multi-die module also comprises a contactless couplerconfigured to convey signals between the first device and the seconddevice. The multi-die module also comprises a coupling loss reductionstructure.

In accordance with at least one example of the disclosure, a multi-diemodule fabrication method comprises obtaining a first die with a firstdevice and obtaining a second die with a second device. The fabricationmethod also comprises providing a contactless coupler configured toconvey signals between the first device and the second device. Thefabrication method also comprises providing a coupling loss reductionstructure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a block diagram of a multi-die module in accordance withvarious examples;

FIG. 2 shows a multi-die module layout in accordance with variousexamples;

FIG. 3 shows an inductive coupler in accordance with various examples;

FIGS. 4A-4D show multi-die module layouts with different coupler lossreduction structures in accordance with various examples;

FIGS. 5A-5B show different die arrangements in accordance with variousexamples;

FIG. 6 shows a graph with different curves representing coupling signalstrength due to different coupling loss reduction structure options inaccordance with various examples;

FIG. 7 shows another graph with different curves representing couplingsignal strength due to different coupling loss reduction structureoptions in accordance with various examples; and

FIG. 8 shows a flowchart of a multi-die module fabrication method inaccordance with various examples.

DETAILED DESCRIPTION

The disclosed examples are directed to multi-die modules that employ acontactless coupler and at least one coupling loss reduction structure.The contactless coupler enables signals to be conveyed between a firstdevice on a first die of the multi-die module and a second device on asecond die of the multi-die module. In at least some examples, the firstdevice of the first die is an oscillator core, and the second device ofthe second die is a resonator.

In different examples, the orientation of the first and second dies in amulti-die module varies. In one example, the first and second dies areoriented such that the first and second devices face each other (e.g.,one of the dies is flipped). In another example, the first and seconddies are oriented such that the first die faces a back side of thesecond die or vice versa. Regardless of die orientation, the contactlesscoupler enables signaling between the first device of the first due andthe second device of the second die.

In some examples, the contactless coupler is an inductive coupler (e.g.,a transformer). In other examples, the contactless coupler is acapacitive coupler (e.g., one or more capacitors). To reduce couplinglosses, disclosed multi-die modules include one or more coupling lossreduction structures. In some examples, a coupling loss reductionstructure is a cavity formed in a die substrate. In other examples, acoupling loss reduction structure is a magnetic material formed betweena contactless coupler component of a given die and the die's substrate.In other examples, a coupling loss reduction structure is a magneticcore between contactless coupler components. In other examples, acoupling loss reduction structure is a redistribution layer (RDL) withat least part of the contactless coupler. In some examples, differentcoupling loss reduction structures are combined. To provide a betterunderstanding, various multi-die module options, contactless coupleroptions, and coupling loss reduction structure options are describedusing the figures as follows.

FIG. 1 shows a block diagram of a multi-die module 100 in accordancewith various examples. As shown, the multi-die module 100 includes afirst die 102 with a first device 104 and a second die 112 with a seconddevice 114. A contactless coupler 105 with contactless couplercomponents 106 and 108 (labeled “CC CPNT” in FIG. 1) is configured toconvey signals between the first device 104 and the second device 114.In different examples, the position and/or layout for each of thecontactless coupler components 106 and 108 varies. In one example, thecontactless coupler component 106 is part of an optional portion 116 ofthe first die 102 and the contactless coupler component 108 is part ofan optional portion 118 of the second die 112. In another example, bothof the contactless coupler components 106 and 108 are part of theoptional portion 116 of the first die 102. In another example, both ofthe contactless coupler components 106 and 108 are part of the optionalportion 118 of the second die 112. In another example, one or both ofthe contactless coupler components 106 and 108 are manufactured separatefrom the first and second dies 102 and 112, and are later coupled to thefirst die 102 and/or the second die 112 as appropriate. In differentexamples, the contactless coupler components 106 and 108 correspond toinductor coils or capacitor terminals.

To reduce signal loss/distortion when signaling with the contactlesscoupler 105, the multi-die module 100 includes coupling loss reductionstructure(s) 120, where each structure 120 can be used together orseparately. In different examples, the coupling loss reductionstructure(s) 120 include a first coupling loss reduction structure 122applied to the first die 102, a second coupling loss reduction structure124 applied to the optional portion 116 of the first die 102, a thirdcoupling loss reduction structure 126 applied to the optional portion118 of the second die 112, and a fourth coupling loss reductionstructure 128 applied between the contactless coupler components 106 and108.

More specifically, in some examples, the first coupling loss reductionstructure 122 corresponds to a cavity formed in a substrate (e.g., ofthe first die 102), where the cavity is aligned with the contactlesscoupler components 106 and 108. In some examples, the cavity is formedby etching a substrate. In some examples, the second coupling lossreduction structure 124 corresponds to a magnetic material on the firstdie 102 between the contactless coupler component 106 and a substrate ofthe first die 102. In other examples, the second coupling loss reductionstructure 124 corresponds to an RDL of the first die 102 that forms atleast part of the contactless coupler component 106. In other examples,the second coupling loss reduction structure 124 corresponds to theabove-noted magnetic material and RDL of the first die 102. In someexamples, the third coupling loss reduction structure 126 corresponds toa magnetic material between the contactless coupler component 108 and asubstrate of the second die 112. In other examples, the third couplingloss reduction structure 126 corresponds to an RDL of the second die 112that forms at least part of the contactless coupler component 108. Inother examples, the third coupling loss reduction structure 126corresponds to the above-noted magnetic material and RDL of the seconddie 112.

In some examples, the fourth coupling loss reduction structure 128corresponds to a magnetic core between contactless coupler components106 and 108 of the contactless coupler 105. In other examples, thefourth coupling loss reduction structure 128 corresponds to an RDLand/or other materials between the contactless coupler components 106and 108. In some examples, one or both of the contactless couplercomponents 106 and 108 are formed on the fourth coupling loss reductionstructure 128. In some examples, the fourth coupling loss reductionstructure 128 is fabricated as part of the first die 102 or the seconddie 112. In other examples, the fourth coupling loss reduction structure128 is fabricated separately from the first die 102 and the second die112. When fabricated separately from the first die 102 and the seconddie 112, the fourth coupling loss reduction structure 128 issubsequently inserted between the first die 102 and the second die 112.If the fourth coupling loss reduction structure 128 includes one or bothcontactless coupler components 106 and 108, then coupling thecontactless coupler components 106 and 108 to respective devices of thefirst die 102 or the second die 112 is performed as appropriate.

In at least some examples, the first device 104 includes an oscillatorcore. Additionally, in some examples, the first device 104 includescircuitry coupled to an oscillator core (e.g., clock components, atransmitter, a receiver, a processing unit, logic blocks, etc.). Indifferent examples, the first device 104 is formed using metal-oxidesemiconductor (MOS) components or bipolar semiconductor components.Meanwhile, in some examples, the second device 114 is amicro-electro-mechanical system (MEMS). In one example, the seconddevice is a bulk-acoustic wave (BAW) resonator. For examples where thefirst device 104 is an oscillator core and the second device 114 is aresonator, the coupling loss reduction structure(s) 120 are provided toensure the quality factor of the multi-die module 100 is higher than apredetermined threshold, which results in compliance with predeterminednoise performance and/or power consumption criteria.

FIG. 2 shows a multi-die module layout 200 in accordance with variousexamples. In the multi-die module layout 200, the first die 102 includesa substrate 202 that extends to line 204. Above line 204 of the firstdie 102 reside device components associated with the first device 104.Meanwhile, the second die 112 is flipped relative to the first die 102and includes a substrate 212 that extends to line 214. Below line 214 ofthe second die 122 reside device components associated with the seconddevice 114.

With the layout 200, device components above line 204 on the first die102 face device components below line 214 on the second device 112 withfillable space 220 between the first die 102 and the second die 112. Indifferent examples, the position of the fillable space 220 relative tothe contactless coupler components 106 and 108 varies. In some examples,fillable space 220 is between the contactless coupler components 106 and108 as shown. In other examples, fillable space 220 is between thecontactless coupler component 106 and the first die 102. In otherexamples, fillable space 220 is between the contactless couplercomponent 108 and the second die 112. Regardless of its position, thefillable space 220 is fillable with a soft non-conductive fillermaterial and/or a rigid non-conductive filler material. As appropriate,the fillable space 220 between contactless coupler components 106 and108, and respective devices on the first die 102 or the second die 112includes connectors (to connect each contactless coupler component witha respective device). In some examples, the contactless couplercomponents 106 and 108 are part of the first die 102 and/or the flippedsecond die 112. In another example, the contactless coupler components106 and/or 108 are part of an RDL and/or other structures that arefabricated separately from the first die 102 and the second die 112, andare later coupled to the first die 102 and/or the second die 112 asappropriate. In one example, the contactless coupler component 106 isconnected to the first die 102 via conductive paths 206 and 208.Likewise, the contactless coupler component 108 is connected to thesecond die 102 via conductive paths 216 and 218. The conductive paths206, 208, 216, 218 correspond to metallic pads, metallic pins, metallayers, and/or solder.

As shown in layout 200, the contactless coupler component 106 resides inthe optional portion 116 of the first die 102. Meanwhile, thecontactless coupler component 108 resides in the optional portion 118 ofthe second die 112. In other examples, both of the contactless couplercomponents 106 and 108 reside in the optional portion 116 of the firstdie 102. In other examples, both of the contactless coupler components106 and 108 reside in the optional portion 118 of the second die 112. Inother examples, one or both of the contactless coupler components 106and 108 reside in an RDL and/or other structures fabricated separatelyfrom the first die 102 and the second die 112. In such case, thecontactless coupler components 106 and 108 are coupled to respectivedevices of the first die 102 and the second die 112 as appropriate.

FIG. 3 shows an inductive coupler 300 in accordance with variousexamples. The inductive coupler 300 is an example of the contactlesscoupler 105 represented in FIG. 1. As shown in FIG. 3, the inductivecoupler 300 comprises first and second contactless coupler components106A and 108A in the form of inductors (e.g., planar inductive coils).Each of the contactless coupler components 106A and 108A includesrespective connection points. More specifically, the connection points206A and 208B for the contactless coupler component 106A are coupled tothe first device 104 of the first die 102 via conductive paths (e.g.,conductive paths 206 and 208 in FIG. 2) regardless of whether thecontactless coupler component 106A is included with the first die 102.Similarly, the connection points 216A and 218B for the contactlesscoupler component 108A are coupled to the second device 114 of thesecond die 112 via conductive paths (e.g., conductive paths 216 and 218in FIG. 2) regardless of whether the contactless coupler component 108Ais included with the second die 104.

FIGS. 4A-4D show multi-die module layouts with different coupling lossreduction structures in accordance with various examples. In FIG. 4A, amulti-die module layout 400A with a coupling loss reduction structure122A is represented. As shown, the first die 102A includes a substrate202A that extends to line 204A. Above line 204A of the first die 102Areside device components associated with the first device 104 (see FIG.1). Meanwhile, the second die 112A is flipped relative to the first die102A and includes a substrate 212A that extends to line 214A. Below line214A of the second die 112A reside device components of the seconddevice 114 (see FIG. 1).

With the layout 400A, device components above line 204A on the first die102A face device components below line 214A on the second die 112A withfillable space 220A between the first die 102A and the second die 112A.In different examples, the position of the fillable spaces 220A relativeto the contactless coupler components 106A and 108A varies. In someexamples, fillable space 220A is between the contactless couplercomponents 106A and 108A as shown. In other examples, fillable space220A is between the contactless coupler component 106A and the first die102A. In other examples, fillable space 220A is between the contactlesscoupler component 108A and the second die 112A. Regardless of itsposition, the fillable space 220A is fillable with a soft non-conductivefiller material and/or a rigid non-conductive filler material. Asappropriate, the fillable space 220A between contactless couplercomponents 106A and 108A, and respective devices on the first die 102Aor the second die 112A includes conductive paths (to connect thecontactless coupler components 106A and 108A with respective devices).In some examples, the contactless coupler components 106A and 108A arepart of the first die 102A and/or the flipped second die 112A. Inanother example, the contactless coupler components 106A and/or 108A arepart of an RDL and/or other structures that are fabricated separatelyfrom the first die 102A and the second die 112A, and are later coupledto the first die 102A and/or the second die 112A as appropriate.

In the layout 400A, the coupling loss reduction structure 122Acorresponds to an etched cavity 402 in the substrate 202A of the firstdie 102A. In different examples, the depth 406 and width 404 of theetched cavity 402 varies. Coupling losses are generally reduced byremoving as much of the substrate 202A aligned with the contactlesscoupler components 106A and/or 108A as possible without compromising thestructural integrity of the first die 102A. In at least some examples,the width 404 is selected based on a size of the contactless couplercomponent 106A and/or 108A (e.g., the width 404 matches the size of thecontactless coupler component 106A and/or 108A, or is greater or lessthan the size of the contactless coupler component 106A and/or 108A by athreshold amount). In at least some examples, the etched cavity 402 hasthe shape of a trapezoid cavity (as in FIG. 4A) due to the etchingprocess. In such case, the width 404 corresponds to the length of theshorter parallel edge of the trapezoid shape (the edge closest to devicecomponents above line 204A). Meanwhile, the longer parallel edge of thetrapezoid shape represented in FIG. 4A is a function of angles 408 and410, and the depth 406. In at least some examples, the angles 408 and410 vary depending on the etching process used to create the etchedcavity 402.

In different examples, the size and/or shape of the etched cavity 402varies. Also, in different examples, the position of the contactlesscoupler components 106A and 108A varies as described herein (e.g., oneis part of the first die 102A and the other is part of the second die112A, both are part of the first die 102A, both are part of the seconddie 112A, one or both are part of an RDL and/or other structuresseparate from the first or second dies 102A and 112B). In at least someexamples, use of a substrate 202A with an etched cavity 402 as in layout400A reduces coupling losses by reducing the amount of conductivematerial in the path of magnetic fields generated during contactlesscoupling operations, which in turn reduces the induced eddy currents andhence the losses.

In FIG. 4B, a multi-die module layout 400B with coupling loss reductionstructures 124A and 126A is represented. As shown, the first die 102Bincludes a substrate 202B that extends to line 204B. Above line 204B ofthe first die 102B reside device components associated with the firstdevice 104 (see FIG. 1). Meanwhile, the second die 112B is flippedrelative to the first die 102B and includes a substrate 212B thatextends to line 214B. Below line 214B of the second die 112B residedevice components associated with the second device 114 (see FIG. 1).

With the layout 400B, device components above line 204B on the first die102B face device components below line 214B on the second device 112Bwith fillable space 220B between the first die 102B and the second die112B. In different examples, the position of the fillable space 220Brelative to the contactless coupler components 106A and 108A varies. Insome examples, fillable space 220B is between the contactless couplercomponents 106A and 108A as shown. In other examples, fillable space220B is between the contactless coupler component 106A and the first die102B. In other examples, fillable space 220B is between the contactlesscoupler component 108A and the second die 112B. Regardless of itsposition, the fillable space 220B is fillable with a soft non-conductivefiller material and/or a rigid non-conductive filler material. Asappropriate, the fillable space 220B between contactless couplercomponents 106A and 108A, and respective devices on the first die 102Bor the second die 112B includes conductive paths (to connect thecontactless coupler components 106A and 108A with respective devices).In some examples, the contactless coupler components 106A and 108A arepart of the first die 102B and/or the flipped second die 112B. Inanother example, the contactless coupler components 106A and/or 108A arepart of an RDL and/or other structures that are fabricated separatelyfrom the first die 102B and the second die 112B, and are later coupledto the first die 102B and/or the second die 112B as appropriate.

In the layout 400B, the coupling loss reduction structure 124Acorresponds to a magnetic material 412 included with an optional portion116A of the first die 102B. More specifically, the magnetic material 412is between the contactless coupler component 106A and the substrate 202Bof the first die 102B. Similarly, the coupling loss reduction structure126A corresponds to a magnetic material 414 included with an optionalportion 118A of the second die 112B. More specifically, the magneticmaterial 414 is between the contactless coupler component 108A and thesubstrate 212B of the second die 112B. In some examples, the magneticmaterials 412 and 414 are made from a combination of Cobalt (Co),Zirconium (Zr), and Tantalum (Ta). In other examples, the magneticmaterials 412 and 414 are made from a combination of Nickel (Ni), Zinc(Zn), and Co ferrites. In other examples, the magnetic materials 412 and414 are made from a combination of Iron (Fe), Co, Silicon (Si), andBoron (B). Other magnetic materials are available as well, includingartificial magnetic surfaces. In some examples, the selection of amagnetic material for the magnetic materials 412 and 414 is based on asignaling frequency between devices of the first and second dies 102Band 112B (see FIG. 1) due to some magnetic materials being frequencysensitive. In at least some examples, use of the magnetic materials 412and/or 414 reduces coupling losses by giving magnetic fields generatedduring contactless coupling operations a flow path that avoids thesubstrates 202B and/or 212B (reducing the amount of conductive materialin the path of magnetic fields generated during contactless couplingoperations).

In FIG. 4C, a multi-die module layout 400C with coupling loss reductionstructures 124B and 126B is represented. As shown, the first die 102Cincludes a substrate 202C that extends to line 204C. Above line 204C ofthe first die 102C reside device components associated with the firstdevice 104 (see FIG. 1). Meanwhile, the second die 112C is flippedrelative to the first die 102C and includes a substrate 212C thatextends to line 214C. Below line 214C of the second die 112C residedevice components associated with the second device 114 (see FIG. 1).

With the layout 400C, device components above line 204C on the first die102C face device components below line 214C on the second device 112Cwith fillable space 220C between the first die 102C and the second die112C. In different examples, the position of the fillable space 220Crelative to the contactless coupler components 106A and 108A varies. Insome examples, fillable space 220C is between the contactless couplercomponents 106A and 108A as shown. In other examples, fillable space220C is between the contactless coupler component 106A and the first die102C. In other examples, fillable space 220C is between the contactlesscoupler component 108A and the second die 112C. Regardless of itsposition, the fillable space 220C is fillable with a soft non-conductivefiller material and/or a rigid non-conductive filler material. Asappropriate, the fillable space 220C between contactless couplercomponents 106A and 108A, and respective devices on the first die 102Cor the second die 112C includes conductive paths (to connect thecontactless coupler components 106A and 108A with respective devices).In some examples, the contactless coupler components 106A and 108A arepart of the first die 102C and/or the flipped second die 112C. Inanother example, the contactless coupler components 106A and/or 108A arepart of an RDL and/or other structures that are fabricated separatelyfrom the first die 102C and the second die 112C, and are later coupledto the first die 102C and/or the second die 112C as appropriate.

In the layout 400C, the coupling loss reduction structure 124Bcorresponds to an RDL 432 included with an optional portion 116B of thefirst die 102C. More specifically, the contactless coupler component106A is formed on a side of the RDL 432 facing the second die 112C. Inother examples, the contactless coupler component 106A is formed on aside of the RDL 432 facing the substrate 202C. Similarly, the couplingloss reduction structure 126B corresponds to an RDL 434 included with anoptional portion 118B of the second die 112C. More specifically, thecontactless coupler component 108A is formed on a side of the RDL 434facing the first die 102C. In other examples, the contactless couplercomponent 108A is formed on a side of the RDL 434 facing the substrate212C. Forming one or both of the contactless coupler components 106A and108A on an RDL (e.g., RDLs 432 or 434) as described herein enables themetal thickness of the contactless coupler components 106A and 108A tobe thicker compared to forming the contactless coupler components 106Aand 108A using other structures of the first die 102C or second die112C. Use of thicker metal to form the contactless coupler components106A and 108A reduces resistivity-related coupling losses duringcontactless coupling operations.

In FIG. 4D, a multi-die module layout 400D with coupling loss reductionstructure 128A is represented. As shown, the first die 102D includes asubstrate 202D that extends to line 204D. Above line 204D of the firstdie 102D reside device components associated with the first device 104(see FIG. 1). Meanwhile, the second die 112D is flipped relative to thefirst die 102D and includes a substrate 212D that extends to line 214D.Below line 214D of the second die 122D reside device componentsassociated with the second device 114 (see FIG. 1).

With the layout 400D, device components above line 204D on the first die102D face device components below line 214D on the second device 112Dwith fillable space 220D between the first die 102D and the second die112D. In different examples, the position of the fillable space 220Drelative to the contactless coupler components 106A and 108A varies. Insome examples, fillable space 220D is between the contactless couplercomponent 106A and the first die 102D, and between the contactlesscoupler component 108A and the second die 112D as shown. Regardless ofits position, the fillable space 220D is fillable with a softnon-conductive filler material and/or a rigid non-conductive fillermaterial. As appropriate, the fillable space 220D between contactlesscoupler components 106A and 108A, and respective devices on the firstdie 102D or the second die 112D includes conductive paths (to connectthe contactless coupler components 106A and 108A with respectivedevices). In some examples, the contactless coupler components 106A and108A are part of the first die 102D and/or the flipped second die 112D.In another example, the contactless coupler components 106A and/or 108Aare part of an RDL and/or other structures that are fabricatedseparately from the first die 102D and the second die 112D, and arelater coupled to the first die 102D and/or the second die 112D asappropriate.

In some examples, the coupling loss reduction structure 128A of layout400D corresponds to a material 452 positioned between the contactlesscoupler components 106A and 108A to reduce coupling losses. In oneexample, the material 452 includes an RDL with one or more of thecontactless coupler components 106A and 108A formed on the RDL. Inanother example, the material 452 corresponds to a magnetic core betweenthe contactless coupler components 106A and 108A, where the position ofthe magnetic core is limited to an active area between the contactlesscoupler components 106A and 108A.

FIGS. 5A-5B show different die arrangements in accordance with variousexamples. In FIG. 5A, various portions for the first die 102 arerepresented, including a substrate 502, first device layers 504 (to formcomponents of the first device 104), backend stack layers (sometimesreferred to as “BEOL” in industry) 506, and RDL 508. The backend stacklayers 506 correspond to metal interconnections and insulative layersabove the first device layers 504, and are used to connect componentsformed by the first device layers 504 together. As desired, additionalcomponents (e.g., contactless coupler components and/or coupling lossreduction structures) are added to the backend stack layers 506.Meanwhile, the RDL 508 corresponds to metal interconnections andinsulative layers to reposition connection points (conductive paths) forcomponents formed by the first device layers 504. As desired, additionalcomponents (e.g., contactless coupler components and/or coupling lossreduction layers) are added to the RDL 508. The RDL 508 connects to thefirst device layers 504 directly or through the backend stack layers506, and facilitates packaging options.

In FIG. 5A, backend stack layers 506 and RDL 508 are part of theoptional portion 116 of the first die 102. In some examples, thecontactless coupler component 106A resides in an upper portion 510A ofthe RDL 508. In other examples, the contactless coupler component 106Aresides in a lower portion 510B of the RDL 508. In other examples, thecontactless coupler component 106A resides in an upper portion 510C ofthe backend stack layers 506. In other examples, the contactless couplercomponent 106A resides in a lower portion 510D of the backend stacklayers 506.

To reduce contactless coupling losses as described herein, a secondcoupling loss reduction structure 124 is added to first die 102. In atleast some examples, the second coupling loss reduction structure 124 ispart of the optional portion 116 of the first die 102. In one example,the second coupling loss reduction structure 124 is a magnetic materialbetween the contactless coupler component 106A and the substrate 502. Inone example, the second coupling loss reduction structure 124 is amagnetic material between the contactless coupler component 106A andanother contactless coupler component (e.g., a magnetic core between thecontactless coupler component 106A and the contactless coupler component108A). In another example, the second coupling loss reduction structure124 is an RDL between the contactless coupler component 106A and thesubstrate 502. In another example, the second coupling loss reductionstructure 124 is an RDL between the contactless coupler component 106Aand another contactless coupler component (e.g., contactless couplercomponent 108A).

In FIG. 5B, various portions of the second die 112 are represented,including a substrate 522, second device layers 524 (corresponding tothe second device 114), backend stack layers 526, and RDL 528. Thebackend stack layers 526 correspond to metal interconnections andinsulative layers above the second device layers 524, and are used toconnect components formed by the second device layers 524 together. Asdesired, additional components (e.g., contactless coupler componentsand/or coupling loss reduction layers) are added to the backend stacklayers 526. Meanwhile, the RDL 528 corresponds to metal interconnectionsand insulative layers to reposition connection points (conductive paths)for components formed by the second device layers 524. As desired,additional components (e.g., contactless coupler components and/orcoupling loss reduction layers) are added to the RDL 528. The RDL 528connects to the second device layers 524 directly or through the backendstack layers 526, and facilitates packaging options.

In FIG. 5B, backend stack layers 526 and RDL 528 are part of theoptional portion 118 of the second die 112. In some examples, thecontactless coupler component 108A resides in an upper portion 530A ofthe RDL 528. In other examples, the contactless coupler component 108Aresides in a lower portion 530B of the RDL 528. In other examples, thecontactless coupler component 108A resides in an upper portion 530C ofthe backend stack layers 526. In other examples, the contactless couplercomponent 108A resides in a lower portion 530D of the backend stacklayers 526.

To reduce contactless coupling losses as described herein, a thirdcoupling loss reduction structure 126 is added to second die 112. In atleast some examples, the third coupling loss reduction structure 126 ispart of the optional portion 118 of the second die 112. In one example,the third coupling loss reduction structure 126 is a magnetic materialbetween the contactless coupler component 108A and the substrate 522. Inone example, the third coupling loss reduction structure 126 is amagnetic material between the contactless coupler component 108A andother contactless coupler components (e.g., a magnetic core between thecontactless coupler component 108A and the contactless coupler component106A). In another example, the third coupling loss reduction structure126 is an RDL between the contactless coupler component 108A and thesubstrate 522. In another example, the second coupling loss reductionstructure 124 is an RDL between the contactless coupler component 106Aand the contactless coupler components 108A.

In some examples, all contactless coupler components for a multi-diemodule (e.g., multi-die module 100) are part of the first die 102 (e.g.,included in the optional portion 116) represented in FIG. 5A. In otherexamples, all contactless coupler components for a multi-die module(e.g., multi-die module 100) are part of the second die 112 (e.g.,included in the optional portion 118) represented in FIG. 5B. In otherexamples, one or more contactless coupler components for a multi-diemodule (e.g., multi-die module 100) are fabricated separately from thefirst die 102 and second die 112, and are later coupled to a respectivedevice of the first die 102 or second die 112 via conductive paths (toconnect the contactless coupler components 106A and 108A with respectivedevices). As desired, fillable space 220 in a multi-die module 100 canbe filled with a soft material (e.g., a silicone-based material) and/ora rigid material (e.g., a plastic or epoxy) as discussed for FIGS.4A-4D.

FIG. 6 shows a graph 600 with curves 602, 604, 606, 608, 610, and 612representing coupler signal strength due to different coupling lossreduction structure options in accordance with various examples. Forgraph 600, each of the curves 602, 604, 606, 608, 610, and 612corresponds to a different substrate cavity size (C1-C6). Morespecifically, curve 602 corresponds to the largest substrate cavity C1(e.g., C1 leaves a substrate thickness of 10 μm below a contactlesscoupler component). Curve 604 corresponds to the next largest substratecavity C2 (e.g., C2 leaves a substrate thickness of 20 μm below acontactless coupler component). Curve 606 corresponds to the nextlargest substrate cavity C3 (e.g., C3 leaves a substrate thickness of110 μm below a contactless coupler component). Curve 608 corresponds tothe next largest substrate cavity C4 (e.g., C4 leaves a substratethickness of 210 μm below the contactless coupler component). Curve 610corresponds to the next largest substrate cavity C5 (e.g., C5 leaves asubstrate thickness of 310 μm below the contactless coupler component).Curve 612 corresponds to the next largest substrate cavity C6 (e.g., C6leaves a substrate thickness of 410 μm below the contactless couplercomponent).

As represented in graph 600, coupling signal strength varies as afunction of frequency and substrate cavity size (the amount of substratematerial below a contactless coupler component). Accordingly, in atleast some examples, a multi-die module employs a coupling lossreduction structure corresponding to a cavity formed in a substrate,where the substrate cavity size below a contactless coupler component isas large as possible without compromising the structural integrity ofthe respective die (a minimum amount of substrate material aligned witha contactless coupler component maximizes signal strength for somesignaling frequencies). In some examples, a non-conductive fillermaterial can be added to an etched cavity to enhance the structuralintegrity of the respective die. In such examples, the substratethickness is reduced compared to scenarios where no filler is used.

FIG. 7 shows a graph 700 with 702, 704, 706, 708, 710, and 712representing coupler signal strength due to different coupling lossreduction structure options in accordance with various examples. Forgraph 700, each of the curves 702, 704, 706, 708, 710, and 712corresponds to a different magnetic material (M1-M6) used for a couplingloss reduction structure as described herein. More specifically, curve702 corresponds to a magnetic material (M1) with a low relativepermeability (e.g., M1 has a relative permeability of 1). Curve 704corresponds to a magnetic material (M2) with a higher relativepermeability than M1 (e.g., M2 has a relative permeability of 5). Curve706 to a magnetic material (M3) with a higher relative permeability thanM2 (e.g., M3 has a relative permeability of 9). Curve 708 to a magneticmaterial (M4) with a higher relative permeability than M3 (e.g., M4 hasa relative permeability of 13). Curve 710 corresponds to a magneticmaterial (M5) with a higher relative permeability than M4 (e.g., M5 hasa relative permeability of 17). Curve 712 corresponds to a magneticmaterial (M6) with a higher relative permeability than M5 (e.g., M6 hasa relative permeability of 20).

As represented in graph 700, coupling signal strength varies as afunction of frequency and the relative permeability of a magneticmaterial used for a coupling loss reduction structure (a higher relativepermeability improves signal strength). Accordingly, in at least someexamples, a multi-die module employs a coupling loss reduction structurewith a magnetic material having a relative permeability appropriate forhigh-frequency signaling. For lower frequency coupler signalingscenarios, the relative permeability of a magnetic material used for acoupling loss reduction structure can be lower.

FIG. 8 shows a flowchart of a multi-die module fabrication method 800 inaccordance with various examples. As shown, the method 800 comprisesobtaining a first die (e.g., die 102) with a first device (e.g., thefirst device 104) at block 802. At block 804, a second die (e.g., die112) with a second device (e.g., the second device 114) is obtained. Atblock 806, a contactless coupler (e.g., the contactless coupler 105)configured to convey signals between the first device and the seconddevice is provided. At block 808, a coupling loss reduction structure(e.g., one or more of the coupling loss reduction structures 122, 124,126, 168) is provided.

In some examples of method 800, providing a coupling loss reductionstructure (block 808) comprises forming a cavity in a substrate of thefirst die, the formed cavity aligned with a position of the contactlesscoupler. More specifically, in some examples, the first device is on afirst side of the first die, and forming the cavity comprises etching anopen cavity on another side of the first die that is opposite the firstside. In some examples of method 800, providing a coupling lossreduction structure (block 808) comprises fabricating the first die orthe second die with a magnetic material between the contactless couplerand a substrate. In some examples, the magnetic material is formedwithin backend stack layers of the first or second die. In otherexamples, the magnetic material is formed above backend stack layers ofthe first or second die. In some examples of method 800, providing acoupling loss reduction structure (block 808) comprises fabricating thefirst die or second die with an RDL that forms at least part of thecontactless coupler. In some examples of method 800, providing acoupling loss reduction structure (block 808) comprises providing amagnetic core for the contactless coupler.

In this description, the term “couple” or “couples” means either anindirect or direct wired or wireless connection. Thus, if a first devicecouples to a second device, that connection may be through a directconnection or through an indirect connection via other devices andconnections. Also, in this description, the recitation “based on” means“based at least in part on.” Therefore, if X is based on Y, then X maybe a function of Y and any number of other factors.

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims. For example,while various figures show a multi-die module layout with a face-to-facearrangement (devices of one die face devices of another die), othermulti-die module layouts are possible (e.g., face-to-back, back-to-back,side-to-side).

What is claimed is:
 1. A multi-die module fabrication method,comprising: obtaining a first die with a first electronic device;obtaining a second die with a second electronic device; providing acontactless coupler configured to convey signals between the firstelectronic device and the second electronic device; and providing acoupling loss reduction structure.
 2. The fabrication method of claim 1,in which providing a coupling loss reduction structure comprises forminga cavity in a substrate of the first die, the cavity aligned with aposition of the contactless coupler.
 3. The fabrication method of claim2, in which the first electronic device is on a first side of the firstdie, and wherein forming the cavity includes etching an open cavity on asecond side of the first die that is opposite the first side.
 4. Thefabrication method of claim 1, in which providing a coupling lossreduction structure includes fabricating the first die or the second diewith a magnetic material between the contactless coupler and asubstrate.
 5. The fabrication method of claim 4, in which the magneticmaterial is formed within a backend stack of the first die or seconddie.
 6. The fabrication method of claim 2, wherein the magnetic materialis formed above a backend stack of the first die or second die.
 7. Thefabrication method of claim 1, in which providing a coupling lossreduction structure includes fabricating the first die or second diewith a redistribution layer (RDL) that forms at least part of thecontactless coupler.
 8. The fabrication method of claim 1, in whichproviding a coupling loss reduction structure includes providing amagnetic core for the contactless coupler.
 9. The fabrication method ofclaim 1, in which the first electronic device includes an oscillatorcore, and the second electronic device includes a resonator.
 10. Thefabrication method of claim 1, in which the contactless coupler is acapacitive coupler.
 11. The fabrication method of claim 1, in which thecontactless coupler is an inductive coupler.
 12. The fabrication methodof claim 1, in which the first die and the second die are arranged suchthat the first electronic device and the second electronic device faceeach other.